linux-kernel - Re: [PATCH] riscv: make ZONE

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Message-ID: <Zu2A1l_cX36sOVcB@infradead.org>
Date: Fri, 20 Sep 2024 07:04:06 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] riscv: make ZONE_DMA32 optional

On Tue, Aug 27, 2024 at 02:36:11PM +0300, Vladimir Kondratiev wrote:
> It is not necessary any RISCV platform has ZONE_DMA32.

That is an odd statement.  The point of ZONE_DMA32 is to make sure
that drivers can always allocate 32-bit DMAable memory, and without
ZONE_DMA32 that is very hard to provide unless you always have an
IOMMU.

> Example - if platform has no DRAM in [0..4G] region,
> it will report failure like below each boot.

ZONE_DMA32 is supposed to contain the 32-bit dma addressable memory,
not 32-bit physical.

Take a look at the changes that just went into Linus' tree for that.